1. Field of the Invention
The present invention relates to a method suitable for forming a silicon-containing deposition film, principally a functional film, and more particularly a non-single crystalline deposition film such as amorphous silicon or polycrystalline silicon adapted for use in semiconductor devices, electrophotographic photosensitive devices, linear image sensors, image pickup devices, photovoltaic devices or the like.
2. Description of the Prior Art
As an example, formation of an amorphous silicon film (hereinafter abbreviated "a--Si") has been tried with various methods such as vacuum evaporation, plasma CVD, CVD, reactive sputtering, ion plating and light CVD. The plasma CVD method is generally employed in industrial application.
However a deposition film composed of amorphous silicon still has many points to be improved, in terms of electrical and optical properties, fatigue characteristic in repeated use, behavior in the atmospheric conditions at use, and productivity or mass-productivity including uniformity and reproducibility.
The reaction involved in the formation of an amorphous silicon deposition film through the conventionally popular plasma CVD method is considerably more complicated than that in the coventional CVD method, and the mechanism thereof has not been fully clarified. Also such deposition film method has many parameters such as temperature of substrate, flow rate and ratio of introduced gasses, pressure at film formation, high-frequency-electric power, structure of electrode, structure of reactor, rate of gas discharge, plasma generating method etc., which in combination often result in unstable plasma generation, eventually giving rise to a significant undesirable effect to the deposited film. Also the manufacturing parameters have to be determined for each apparatus, so that it has been difficult to generalize such manufacturing conditions. However the use of the plasma CVD method is presently accepted as the best for obtaining an amorphous silicon film with satisfactory electrical, optical, photoconductive or mechanical properties required in various applications.
In certain applications requiring high-speed reproducible mass production while sufficiently achieving a larger film with uniform thickness and quality, there is required a significant capital investment in the mass production equipment for the formation of amorphous silicon deposition film through the plasma CVD method, with complex control parameters of narrow control tolerances, and the equipment itself requires delicate control. On the other hand, the conventional technology with the ordinary CVD method requires a high temperature and is unable to provide a practically acceptable deposition film.
As explained in the foregoing, there has been long desired a method capable of mass producing the amorphous silicon film with inexpensive equipment, while maintaining the uniformity and other properties required in the application. The same requirements exist also for other functional films, such as films of silicon nitride, silicon carbide, or silicon oxide.
The present invention, therefore, is to provide a novel method of film deposition, which is free from the above-mentioned drawbacks of the plasma CVD method and is not dependent on the conventional technologies.